Getting number of certain days-of-the-week (weekend) from interval in PostgreSQL

Question

Given 2 timestamps in postgres, how do you calculate the time difference without counting whole Saturdays and Sundays?

OR

How do you count the number of Satu

Answer 1

This should answer the second part of your question:

create or replace function is_weekend_day(date) returns boolean
 strict immutable language 'sql'
 as $$ select case extract(dow from $1) when 0 then true when 6 then true else false end $$;

create or replace function count_weekend_days(start_date date, end_date date) returns int
 strict immutable language 'sql'
 as $$
select cast(sum(case when is_weekend_day($1 + ofs) then 1 else 0 end) as int)
from generate_series(0, $2 - $1) ofs
$$;

Making a corresponding count_non_weekend_days is simple after that.